Genetic Basis, Transferability And Linkage Of Streptomycin And Sulphonamide Resistance Genes In Escherichia Coli From Food Animals In Kenya

Abstract

The genetic basis and transferability of streptomycin and sulphonamide resistance was studied in 23 Escherichia coli isolates from food animals in Kenya. Physical linkage of the streptomycin resistance gene strA with sulphonamide resistance gene sul2 was investigated by PCR and confirmed by sequencing. Two small plasmids of 6 kb (pSSGK1) and 8 kb, (pSSTGK1) identified by transformation to mediate resistance to at least streptomycin and sulphonamide were restricted in order to define their relatedness. Their restriction maps were compared to one another and with the maps of other plasmids from E. coli known to mediate these resistance properties. Streptomycin resistance was based on the expression of the strA, strB and/or aadA1 genes, while sulphonamide resistance was encoded by the sul2 or sul1 gene. The strA, strB and sul2 genes were transferable via conjugation and transformation. Physically linked sul2 and strA genes were present in both plasmids pSSGK1 and pSSTGK1. The plasmids pSSGK1 and pSSTGK1 were different from each other, but similar respectively to sulphonamide/streptomycin and sulphonamide/streptomycin/tetracycline resistance plasmids described previously in uropathogenic E. coli from humans. Conjugation of plasmids encoding streptomycin and sulphonamide resistance may be one mechanism for the wide dissemination and persistence of these resistances among food animal E. coli in Kenya. Physical linkage of the plasmid-borne strA and sul2 genes would facilitate the spread of these genes by co-selection during selective pressure imposed by the use either of the two antimicrobials and highlights the need for the prudent use of streptomycin or sulphonamides in animal husbandry.